1. Field of the Invention
This invention relates to well tools used in the rotary drilling of wellbores, and it more particularly relates to a shock absorber device.
2. Background Art
In the drilling of a wellbore, a rotary drill bit is employed for cutting away the formations being penetrated. The drill bit is suspended upon a drill string which can be of great length, e.g. 25,000 feet. Although the drill bit rotates at relatively low RPM, it can generate relatively large angular and axial shock forces that are applied to the drill string. These shock forces can cause physical injury to both the drill string and drill bit. Also, these shock forces may cause the drill bit to lose contact with the bottom of the wellbore. As a result, the drilling efficiency can suffer from even small axial displacements (e.g., one half inch) of the drill bit from contact with the formation being penetrated. Likewise, angular shocks produce serious variations in the torque applied to the drill bit which results in non-uniform formation penetration. Obviously, it is most desirable to prevent these angular and axial shock forces from being applied to the drill string or effecting the bottom hole contact of the drill bit.
Various well tools have been proposed to have either bottom hole contact or shock absorber functions. A few well tools have been proposed to provide a combination of such functions. In general, these combination tools use a helical connection in the well tool and a fluid dash pot or hydraulic cushion. As a result, these combination tools are very complex in construction and element functioning which leads to short operational lives, difficult field servicing, repairs and other undesirable results.
U.S. Pat. No. 4,443,206 to the inventor of the present invention provides a well tool maintaining bottom hole contact and absorbing shocks with a relatively simple construction, long life in well drilling and a relatively simple, easily repaired structure. However, it would be desirable to further increase the life of a tool of this kind.